1. Field of the Invention
This invention relates to an apparatus having a device which judges whether a frame is exposed or not in a film, wherein photographing information is recorded at a recording section, which is arranged correspondingly to each film frame, when the film frame is exposed.
2. Description of the Prior Art
Conventionally, a camera has been known wherein a film, which is contained in a cartridge and provides a recording section capable of recording photographing information on each film frame correspondingly, is loaded, and magnetic recording is executed on the recording section, feeding out the film from the cartridge. In such a camera, the camera is capable of re-using a film after rewinding it in a state in which not all of the frames are photographed (exposed), and loading the film cartridge again in the camera, and feeding the film out to an unexposed frame. In order to re-use a film in this manner, the camera needs to have a functional construction for detecting a recorded information signal in a recording section corresponding to each film frame, and judging whether the frame is exposed or not.
However, according to such an above-mentioned recording section made of magnetic substance and the like, which is provided on a photographing film for a camera, it is difficult to pick up signal strength efficiently in characteristics of magnetic recording and outputting, compared with a magnetic recording tape used for an ordinary audio cassette tape recorder and the like. Therefore, even though a magnetic signal is recorded on the recording section, it tends to be difficult to judge whether a magnetic signal is recorded or not by comparing small and large portions in the signal's amplitude because a signal to noise ratio (hereinafter refers to as S/N ratio) is likely to be reduced due to a small difference in the amplitude of noise portion and magnetic signal portion.
For example, in FIG. 4, FIG. 4 (a) shows a magnetic output in a noise portion, and FIG. 4 (b) shows a magnetic output in a signal portion. At the noise portion, noise of a motor, CRT and the like peripheral to the recording section is picked up, and at the signal portion, a reduction of magnetic output signal is caused by azimuth variations of a magnetic head and unevenness in the operation of electronic components of a circuit. As a result, the S/N ratio is reduced. Further, when the magnetic output signal at the signal portion is reduced as a whole, there is little signal which is beyond a threshold value and hence it may be judged incorrectly.
Furthermore, if a detection whether a magnetic recording exists or not is executed regardless a kind of film, it is likely to be an incorrect detection, because the magnetic output signal level varies considerably due to difference in characteristic of a kind of film (for example, negative films or positive films).
Furthermore, there is an abnormality in which only one part of film frames is not exposed or signal level of magnetic recording is reduced in the middle of exposed frames. In such cases, this problem is likely to cause an incorrect operation if such abnormal frame, which is detected as an unexposed film at first, is fed to its lead portion immediately after judging whether a frame is not exposed or exposed by analyzing the frames one by one.